Some modem digital telecommunication systems are multi-carrier systems where a number of carrier waves at different frequencies are used to transit information within the same time slot. A typical multi-carrier system comprises a central unit that handles the communication with and between a number of subscribers within a particular area. Such systems can also be used in, for example, office environments, in so-called LAN-systems (Local Area Network).
The multi-carrier technique demands a relatively high power supply for transmission because the amplifiers that are used in such systems have a low efficiency rating. Many types of equipment used for wireless communication in office environments, for example, portable computers and PDAs (Personal Digital Assistant) have power sources with extremely limited capacity, which means that it is difficult to use such equipment in multi-carrier systems. But it is still desirable to use, for example, portable computers and PDAs for wireless communication in systems where the multi-carrier technique is used.
The present invention makes it possible for equipment with a limited power supply to be incorporated in a multi-carrier system. A central unit for a multi-carrier system includes equipment for receiving a signal with multiple carrier waves, and equipment for receiving a signal with one carrier wave (single-carrier). The one carrier wave is one of the carrier waves is included in the multi-carrier system.
Because single carrier frequency transmission can be carried out in a more energy-efficient way than multi-carrier transmission, equipment that cannot communicate with the central unit in a multi-carrier system on account of limitations in its power supply can nonetheless transmit to the central unit transmission on a single frequency. The reception of multi-carrier signals does not require as much power as transmission, which means that equipment units with limited power can receive transmissions from the central unit in a multi-carrier system in the same way as other equipment units in the system. The fact that single-carrier units in the system transmit on one of the carrier waves that is already included in the multi-carrier system for which the central unit is designed means that the modifications that need to be made to a central unit to function according to the invention are small.
In addition to being provided with equipment for the reception of signals on a single carrier wave, the central unit may be equipped with a scheduler for scheduling transmissions from a single-carrier unit in interaction with this unit. The interaction with the single-carrier equipment for the scheduling of its transmissions may be carried out by modifying existing data frames used for scheduling communication within the multi-carrier system in which the central unit is incorporated. Single-carrier equipment is also provided that is equipped with means for scheduling its own transmissions to the central unit in interaction with a central unit in a multi-carrier system, preferably a central unit according to the invention.